Unbalanced forces generated by an asymmetric attachment of microtubules promote segregation of merotely toward the correct pole in anaphase. (A, top) The merotelic (upper) kinetochore is attached asymmetrically and segregates to the correct pole (category I). (bottom) Example of a simulation corresponding to this category, the SPBs trajectories are in black. At anaphase onset (12 min), most kinetochores rapidly segregate to the poles (light green and gray traces), whereas the merotelic kinetochore (dark green trace) lags behind and regains the correct pole with a delay. (B, top) The merotelic (upper) kinetochore is attached symmetrically (asterisk) and fails to segregate, resulting in the cut phenotype as shown by the dark red line in the simulation below (category II). (C, top) The merotelic (upper) kinetochore is attached asymmetrically and slowly moves to the wrong pole as shown by the dark blue line in the simulation below (category III). Closed arrows indicate direction of chromosome movement. (D) Statistical analysis of the relative proportions of the three phenotypes generated by merotelic attachment in anaphase (n = 45,100 simulations) analyzed as a function of the kinetochore orientation parameter value β. Error bars represent the SD of the error rate for the 250 simulations used for each value of β.